Hardener composition for epoxy resins

ABSTRACT

A hardener composition useful for curing epoxy resins including a blend of (a) a carboxylic anhydride which is a copolymer of an ethylenically unsaturated anhydride and a vinyl compound; (b) a copolymer of an ethylenically unsaturated anhydride and an elastomer; and optionally (c) a stabilizing agent such as a block copolymer to prevent phase separation of components (a) and (b). The hardener composition is particularly useful in electrical laminates applications.

FIELD OF THE INVENTION

The present invention relates to compositions useful as crosslinkers forcuring epoxy resins. More particularly, the present invention relates toa hardener composition useful as a crosslinker for curing epoxy resins.The epoxy resins, in turn, are used for example, in electrical laminatesapplications.

BACKGROUND OF THE INVENTION

It is known to make electrical laminates and other composites from afibrous reinforcement and an epoxy-containing matrix resin. Examples ofsuitable processes usually contain the following steps:

(1) An epoxy-containing formulation is applied to or impregnated into asubstrate by rolling, dipping, spraying, other known techniques and/orcombinations thereof. The substrate is typically a woven or nonwovenfiber mat containing, for instance, glass fibers or paper.

(2) The impregnated substrate is “B-staged” by heating at a temperaturesufficient to draw off solvent in the epoxy-containing formulation andoptionally to partially cure the epoxy-containing formulation, so thatthe impregnated substrate can be handled easily. The “B-staging” step isusually carried out at a temperature of from 90° C. to 210° C. and for atime of from 1 minute to 15 minutes. The impregnated substrate thatresults from B-staging is called a “prepreg.” The temperature is mostcommonly 100° C. for composites and 130° C. to 200° C. for electricallaminates.

(3) One or more sheets of prepreg are stacked or laid up in alternatinglayers with one or more sheets of a conductive material, such as copperfoil, if an electrical laminate is desired.

(4) The laid-up sheets are pressed at high temperature and pressure fora time sufficient to cure the resin and form a laminate. The temperatureof this lamination step is usually between 100° C. and 230° C., and ismost often between 165° C. and 200° C. The lamination step may also becarried out in two or more stages, such as a first stage between 100° C.and 150° C. and a second stage at between 165° C. and 190° C. Thepressure is usually between 50 N/cm² and 500 N/cm². The lamination stepis usually carried out for a time of from 1 minute to 200 minutes, andmost often for 45 minutes to 90 minutes. The lamination step mayoptionally be carried out at higher temperatures for shorter times (suchas in continuous lamination processes) or for longer times at lowertemperatures (such as in low energy press processes).

Optionally, the resulting laminate, for example, a copper-clad laminate,may be post-treated by heating for a time at high temperature andambient pressure. The temperature of post-treatment is usually between120° C. and 250° C. The post-treatment time usually is between 30minutes and 12 hours.

It is conventional in the preparation of epoxy-containing laminates toincorporate into an epoxy resin composition a hardener (also referred toas a “curing agent” or a “crosslinking agent”) in order to provide thecrosslinking of the epoxy composition to form a thermoset resin. Varioushardeners for epoxy resins are generally known including amines,phenolics, anhydrides, carboxylic acids, mercaptans and isocyanates.Epoxy resins can also homopolymerize by reacting with both nucleophilicand electrophilic species.

The current trend of the electrical laminates industry requiresmaterials with improved dielectric properties including lower dielectricconstant (Dk) and loss factor (Df); superior thermal propertiesincluding high glass transition temperature (Tg) and decompositiontemperature (Td); and good processability. One known approach forimproving laminate properties consists of curing a flame retardant epoxyresin with an anhydride hardener such as styrene-maleic anhydridecopolymer (SMA). For example, the use of SMA as cross-linking agents forepoxy resins is described in U.S. Patent Application Publication No.2002/0082350 A1. The main drawback of this known SMA hardener system isthat it provides laminates with high brittleness. The known SMA hardenersystem also has poor processability because a prepreg powder made withthe known SMA hardener is easy to remove from a substitute such as aglass web, creating a lot of dust when the prepreg is handled (aso-called “mushroom” effect). In addition, the resulting laminate madefrom the known SMA hardener system has a low toughness and is easy todelaminate, creating defects during drilling operations of thelaminates. Often, the resulting prepreg also shows poor prepregcosmetics due to entrapped gas bubbles.

It is therefore desired to provide a hardener system for epoxy resinswithout the disadvantages of the prior art.

SUMMARY OF THE INVENTION

One aspect of the present invention is directed to a hardenercomposition for epoxy resins, for example, epoxy resins used in themanufacture of electrical laminates. The hardener composition includes ablend of (a) a carboxylic anhydride which is a copolymer of anethylenically unsaturated anhydride and a vinyl compound such as, forexample, styrene-maleic anhydride (SMA) copolymer, (b) a copolymer of anethylenically unsaturated anhydride and an elastomer such as, forexample, a maleic anhydride-modified polybutadiene (PBMA), and,optionally, (c) a stabilizing agent, such as, for example, astyrene-butadiene-methyl methacrylate triblock polymer (SBM), to preventphase separation of the SMA and PBMA. The components (a), (b), and (c),when present, are present in the blend at a preferred ratio to maintainthe preferred properties of the hardener and the epoxy resin in whichthe hardener is used.

Another aspect of the present invention is directed to a curable epoxyresin composition containing the hardener composition described above.

Still another aspect of the present invention is directed to a prepregor a laminate made from the above curable epoxy resin composition.

When the hardener composition of the present invention is used in anepoxy resin/hardener system, several advantages are obtained includingfor example, (i) an epoxy resin composition that will not have phaseseparation between the epoxy component and the additive components inthe resin composition; (ii) an epoxy/hardener varnish which is a clearsolution or a stable dispersion depending on the solvent used when anappropriate ratio of components (a), (b), and (c) is used; (iii) apartly cured B-staged prepreg that has improved prepreg propertiesincluding for example, an improved surface appearance and generates lessdust during handling compared to standard SMA epoxy systems; (iv) afully cured C-staged laminate that exhibits improved laminate propertiesincluding for example, improved toughness and less tendency todelaminate compared to standard SMA/epoxy systems or compared to epoxyresin systems with standard toughening agents; (v) a laminate havingimproved dielectric properties; and (vi) a laminate with enhancedthermal properties including for example, a high glass transitiontemperature and a high thermal resistance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Generally, the hardener system of the present invention includes a blendof (a) a carboxylic anhydride which is a copolymer of an ethylenicallyunsaturated anyhydride and a vinyl compound, (b) a copolymer of anethylenically unsaturated anhydride and an elastomer and, optionally,(c) a stabilizing agent, in the appropriate amounts to provide aneffective hardener composition for epoxy resins.

The hardener composition of the present invention includes component (a)defined as a copolymer of (i) an ethylenically unsaturated anhydride,and (ii) a vinyl compound.

Copolymers of an ethylenically unsaturated anhydride and a vinylcompound, include for example, styrene-maleic anhydride copolymer (SMA)and others, for example, as described in WO 95/06075, incorporatedherein by reference.

Copolymers of styrene and maleic anhydride having a molecular weight(M_(w))in the range of from 1500 to 50,000 and an anhydride content ofmore than 15 percent are particularly preferred. Commercial examples ofthese copolymer materials include SMA 1000, SMA 2000, SMA 3000 and SMA4000 having styrene-maleic anhydride ratios of 1:1, 2:1, 3:1 and 4:1respectively and molecular weight ranging from 6,000 to 15,000; and arecommercially available from Atofina.

The hardener composition of the present invention also includescomponent (b) which is a copolymer of an etheylically unsaturatedanhydride and an elastomer such as for example, a maleinizedpolybutadiene (PBMA). The PBMA used in the present invention may be acommercial available PBMA product such as Ricon® MA resins commerciallyavailable from Sartomer. The maleinized polybutadiene used in thepresent invention may also be prepared according to various knowntechniques for example by the reaction of polybutadiene with maleicanhydride as described in U.S. Patent Nos. 4,028,437; 4,601,944; and5,300,569, incorporated herein by reference.

The amounts of SMA and PBMA used in the hardener composition are suchthat the SMA to PBMA weight ratio is between about 99:1 and about 70:30,and preferably between about 95:5 and about 80:20.

The optional stabilizing agent, component (c) of the present invention,includes among others block copolymers with at least one block misciblewith the dispersed phase and at least one block miscible with thecontinuous phase in order to avoid macro phase-separation. An example ofa preferred stabilizing agent is a triblock polymer,styrene-co-butadiene-co-methyl methacrylate (SBM). The optionalstabilizing agent is preferably added to the hardener composition of thepresent invention because without a stabilizing agent, the SMA/PBMAsystem phase separates. On the other hand, when SBM is used in thepresent hardener composition in the appropriate amount to form theappropriate ratio between SMA/PBMA/SBM, the hardener system of thepresent invention is a stable turbid dispersion (no phase separation andno settling).

The amounts of stabilizing agent when used in the hardener compositionare such that the ratio of PBMA to stabilizing agent is generallybetween about 50:50 and about 99:1, preferably between about 60:40 andabout 95:5, more preferably between about 75:25 and about 85:15.

The hardener composition may be dissolved in a solvent or a blend ofsolvents. Examples of suitable solvents include among others ketones,ethers, acetates, aromatic hydrocarbons, dimethylformamide, andcyclohexanone.

The hardener composition of the present invention may containingredients in addition to the hardener components discussed above. Forexample, the hardener composition may contain other differentcrosslinking agents, i.e. co-crosslinkers, such as those selected fromthe other known hardeners for epoxy resins including amines, phenolics,anhydrides, carboxylic acids, mercaptans and isocyanates.

Any of the well known co-crosslinkers described in U.S. Pat. Nos.4,042,550 and 3,789,038, incorporated herein by reference, may be usedin the present invention. As an illustration, known co-crosslinkers thatmay be used in the present invention, include for example, carboxylicacids such as oxalic acid, phthalic acid, terphthalic acid, and succinicacid; and anhydrides such as phthalic anhydride, succinic anhydride,hexahydrophthalic anhydride, tetrahydrophthalic anhydride, nadicanhydride and maleic anhydride.

The amount of co-crosslinker present in the hardener composition may besuch that the SMA to co-crosslinker weight ratio is between about 99:1and about 50:50, and preferably between about 95:5 and about 75:25.

The hardener composition of the present invention may be produced bymixing all of the components of the composition together in any order,preferably in solution form for example by dissolving the components ina solvent at a temperature of from about 20° C. and above; andpreferably from about 20° C. to about 150° C.; and more preferably fromabout 60° C. to about 100° C. When the hardener solution is prepared ata low temperature, e.g. about ambient temperature (−250° C.), it takes alonger time for the components to dissolve in the solvent.

The hardener composition described above is advantageously used incombination with an epoxy resin to form a curable epoxy resincomposition. The hardener composition of the present invention providescrosslinking between the hardener and the epoxy moieties of the epoxyresin to form a thermoset resin.

The epoxy resin component used in the curable epoxy resin composition isa polyepoxide. The polyepoxide compound useful in the practice of thepresent invention is suitably a compound which possesses more than one1,2-epoxy group. In general, the polyepoxide compound is a saturated orunsaturated aliphatic, cycloaliphatic, aromatic or heterocyclic compoundwhich possesses more than one 1,2-epoxy group. The polyepoxide compoundcan be substituted with one or more substituents such as lower alkylsand halogens. Such polyepoxide compounds are well known in the art.Illustrative polyepoxide compounds useful in the practice of the presentinvention are described in the Handbook of Epoxy Resins by H.E. Lee andK. Neville published in 1967 by McGraw-Hill, New York and U.S. Pat. No.4,066,628, incorporated herein by reference.

Particularly useful polyepoxide compounds which can be used in thepractice of the present invention are polyepoxides having the followinggeneral formula:

wherein R is substituted or unsubstituted aromatic, alphatic,cycloaliphatic or heterocyclic polyvalent group and n had an averagevalue of from 1 to less than about 8.

As an illustration of the present invention, examples of known epoxyresins that may be used in the present invention, include for example,the diglycidyl ethers of resorcinol, catechol, hydroquinone, bisphenol,bisphenol A, bisphenol AP (1,1-bis(4-hydroxylphenyl)-1-phenyl ethane),bisphenol F, bisphenol K, tetrabromobisphenol A, phenol-formaldehydenovolac resins, alkyl substituted phenol-formaldehyde resins,phenol-hydroxybenzaldehyde resins, cresol-hydroxybenzaldehyde resins,dicyclopentadiene-phenol resins, dicyclopentadiene-substituted phenolresins tetramethylbiphenol, tetramethyl-tetrabromobiphenol,tetramethyltribromobiphenol, tetrachlorobisphenol A and any combinationthereof.

Examples of diepoxides particularly useful in the present inventioninclude diglcidyl ether of 2,2-bis(4-hydroxyphenyl) propane (generallyreferred to as bisphenol A) and diglycidyl ether of2,2-bis(3,5-dibromo-4-hydroxyphenyl) propane (generally referred to astetrabromobisphenol A). Mixtures of any two or more polyepoxides canalso be used in the practice of the present invention.

Other useful epoxide compounds which can be used in the practice of thepresent invention are cycloaliphatic epoxides. A cycloaliphatic epoxideconsists of a saturated carbon ring having an epoxy oxygen bonded to twovicinal atoms in the carbon ring for example as illustrated by thefollowing general formula:

wherein R is as defined above and n is as defined above.

The cycloaliphatic epoxide may be a monoepoxide, a diepoxide, apolyepoxide, or a mixture of those. For example, any of thecycloaliphatic epoxide described in U.S. Pat. No. 3,686,359,incorporated herein by reference, may be used in the present invention.As an illustration, the cycloaliphatic epoxides that may be used in thepresent invention include, for example,(3,4-epoxycyclohexyl-methyl)-3,4-epoxy-cyclohexane carboxylate,bis-(3,4-epoxycyclohexyl) adipate, vinylcyclohexene monoxide andmixtures thereof.

The ratio of polyepoxide to hardener used in the epoxy resin compositionof the present invention is such that the thermal properties of theresulting thermoset resin are maintained. The amounts of the hardenercomposition employed in the epoxy resin composition are such that theepoxy to hardener molar ratio is between about 0.5:1.0 and about2.0:1.0, preferably between about 0.8:1.0 and about 1.2:1.0 and mostpreferably between about 0.9:1.0 and about 1.1:1.0.

In addition to the polyepoxide and hardener composition, the epoxy resincomposition of the present invention may include a catalyst as anoptional component. The catalyst may be a single component or acombination of two or more different catalysts. Catalysts useful in thepresent invention are those catalysts which catalyze the reaction of apolyepoxide with a cross-linker, and which remain latent in the presenceof an inhibitor at lower temperatures. Preferably the catalyst is latentat temperatures of about 140° C. or below, and more preferably at about150° C. or below. Latency is demonstrated by an increase of at leastabout 10 percent in gel time as determined by a stroke cure testperformed at about 150° C. to about 170° C. Examples of preferredcatalysts are compounds containing amine, phosphine, heterocyclicnitrogen, ammonium, phosphonium, arsonium or sulfonium moieties.Examples of more preferred catalysts are the heterocyclic nitrogen andamine containing compounds and even more preferred compounds areheterocyclic nitrogen containing compounds.

Any of the well known catalysts described in U.S. Pat. No. 4,925,901,incorporated herein by reference, may be used in the present invention.As an illustration, examples of the known catalysts that may be used inthe present invention, include for example, suitable onium or aminecompounds such as ethyltriphenyl phosphonium acetate, ethyltriphenylphosphonium acetate-acetic acid complex, triethylamine, methyldiethanolamine, benzyldimethylamine, and imidazole compounds such as2-methylimidazole and benzimidazole.

The catalysts, when present, are employed in a sufficient amount toresult in a substantially complete cure of the epoxy resin, with somecross-linking. For example, the catalyst may be used in an amount offrom about 0.01 to about 5 parts per hundred parts of resin, with fromabout 0.01 to about 1.0 parts per hundred parts of resin being preferredand from about 0.02 to about 0.5 catalyst per hundred parts of resinbeing more preferred.

Concentrations of components used to describe in the present inventionare measured as parts by weight of components per hundred parts of resinby weight (phr), unless otherwise noted. The “resin” in the definitionof “phr” herein refers to the polyepoxide and the hardener together inthe composition.

Another optional component useful in the epoxy resin composition of thepresent invention is a reaction inhibitor. The reaction inhibitor mayinclude boric acid, Lewis acids containing boron such as alkyl borate,alkyl borane, trimethoxyboroxine, an acid having a weak nucleophilicanion, such as, perchloric acid, tetrafluoboric acid, and organic acidshaving a pKa from 1 to 3, such as, salicylic acid, oxalic acid andmaleic acid. Boric acid as used herein refers to boric acid orderivatives thereof, including metaboric acid and boric anhydride; andcombinations of a Lewis acid with boron salts such as alkyl borate ortrimethoxyboroxine. When an inhibitor is used in the present invention,boric acid is preferably used. The inhibitor and catalyst may beseparately added, in any order, to the epoxy resin composition of thepresent invention, or may be added as a complex.

The amount of the inhibitor present relative to the catalyst in theepoxy resin composition of the present invention can be adjusted toadjust the gel time of the epoxy resin composition. At constant levelsof catalyst, an increasing amount of inhibitor will yield acorresponding increase in the gel time. At a desired catalyst level therelative amount of inhibitor can be decreased to decrease the gel time.To increase the gel time the amount of inhibitor can be increasedwithout changing the catalyst level.

The molar ratio of inhibitor (or mixture of different inhibitors) tocatalyst is that ratio which is sufficient to significantly inhibit thereaction of the polyepoxide as exhibited by an increase in gel time ascompared to a like composition free of inhibitor. Simple experimentationcan determine the particular levels of inhibitor or mixtures which willincrease in gel time but still allow a complete cure at elevatedtemperatures. For example, a preferable molar ratio range of inhibitorto catalyst where up to about 5.0 phr of boric acid is used, is fromabout 0.1:1.0 to about 10.0:1.0, with a more preferred range being fromabout 0.4:1.0 to about 7.0:1.0.

Another optional component which may be added to the epoxy resincomposition of the present invention is a solvent or a blend ofsolvents. The solvent used in the epoxy resin composition is preferablymiscible. In addition, an epoxy/hardener varnish containing the hardenercomposition of the present invention is a clear solution or a stabledispersion depending on the optional solvents used in the composition.Examples of suitable solvents employed in the present invention includefor example ketones, ethers, acetates, aromatic hydrocarbons,cyclohexanone, dimethylformamide and combinations thereof.

Preferred solvents for the catalyst and the inhibitor are polarsolvents. Lower alcohols having from 1 to 20 carbon atoms, such as forexample methanol, provide good solubility and volatility for removalfrom the resin matrix when prepregs are formed.

Polar solvents are particularly useful to dissolve inhibitors of boricacid or Lewis acids derived from boron. If the polar solvents arehydroxy containing, there exists a potential competition for availablecarboxylic acid anhydride between the hydroxy moiety of the solvent andthe secondary hydroxyl formed on opening of the oxirane ring. Thus,polar solvents which do not contain hydroxyl moieties are useful, forexample, N,-methyl-2-pyrrolidone, dimethylsulfoxide, dimethylformamide,and tetrahydrofuran. Also useful are dihydroxy and trihydroxyhydrocarbons optionally containing ether moieties or glycol ethershaving two or three hydroxyl groups. Particular useful are C₂₋₄ di- ortrihydroxy compounds, for example 1,2-propane diol, ethylene glycol andglycerine. The polyhydroxy functionality of the solvent facilitates thesolvent serving as a chain extender, or as a co-cross-linker accordingto the possible mechanism previously described concerningco-cross-linkers.

The total amount of solvent used in the epoxy resin compositiongenerally may be between about 20 and about 60 weight percent,preferably between about 30 and about 50 weight percent, and mostpreferably between about 35 and about 45 weight percent.

The curable epoxy resin composition according to the present inventionmay contain usual additives such as fillers, dyes, pigments, thixotropicagents, surfactants, fluidity control agents, stabilizers, diluents thataid processing, adhesion promoters, flexibilizers, toughening agents andfire retardants.

The curable epoxy resin composition of the present invention can beproduced by mixing all the components of the composition together in anyorder. Alternatively, the curable epoxy resin composition of the presentinvention can be produced by preparing a first composition comprisingthe epoxy resin component and a second composition comprising thehardener composition component. All other components useful in makingthe epoxy resin composition may be present in the same composition, orsome may be present in the first composition, and some in the secondcomposition. The first composition is then mixed with the secondcomposition to form the curable epoxy resin composition. The epoxy resincomposition mixture is then cured to produce an epoxy resin thermosetmaterial. Preferably, the curable epoxy resin composition is in the formof a solution wherein the components of the composition are dissolved ina solvent. Such solution or varnish is used for producing a coatedarticle.

The curable epoxy resin composition of the present invention may be usedto coat any article for which a coating is desired. The article may becoated with the composition of the present invention using any methodknown to those skilled in the art, including for example powder-coating,spray-coating, and contacting the article with a bath containing thecomposition. Such article can be coated, with the epoxy resincomposition, and the coating can be partially cured or fully cured. Inthe embodiment where the coating is partially cured, the article may befurther processed such that the partially cured resin may be finallycured. The article coated can be any substrate, for example metal,cement and reinforcing material. In one embodiment, the article is afibrous reinforcing material for composites, prepregs or laminates.

The curable epoxy resin composition according to the present inventioncan be employed to make composites for, inter alia, the electronics,construction, aviation, and automobile industries. The curable epoxyresin composition of the present invention may be used to make compositematerials by techniques well known in the industry such as byimpregnating a reinforcing material with molten or dissolved resin, orvia resin transfer molding, filament winding, pultrusion or RIM(reaction injection molding) and other moulding, encapsulation, orcoating techniques. Also, the curable epoxy resin compositions accordingto the present invention can be employed wherever use is made ofconventional epoxy resins, such as a glue, coating, molding resin,embedding resin, encapsulating resin, sheet molding compound, or bulkmolding compound.

The epoxy resin composition of the present invention is particularlyuseful for making B-staged prepegs and laminates, for example forprinted wiring boards, by well known techniques in the industry. Thepresent invention is preferably directed to laminates for use in theelectronics industry incorporating the epoxy resin composition of thepresent invention. It was found that even when the resin composition isbased on simple difunctional epoxy compounds, the combination of resincomponents according to the present invention will give excellentproperties for application in the electronics industry.

Generally, laminates for use in the electronics industry, particularlyfor printed wiring boards, are produced by impregnating a supporting orreinforcing material with the epoxy resin composition of the presentinvention, followed by the resin being cured wholly or in part. Areinforcing material impregnated with a partially cured resin is usuallyreferred to herein as the “prepeg”. To make a printed wiring board fromprepegs, one or more layers of prepegs are laminated with, for example,one or more layers of a metallic material such as copper.

The reinforcing material which may be impregnated with the epoxy resincomposition of the present invention include any material which would beused by the skilled artisan in formation of composites, prepregs andlaminates. Examples of the forms of such reinforcing materials are wovenfabric, cloth, mesh, web, or fibers; or in the form of a cross-plylaminate of unidirectionally oriented parallel filaments. Generally,such reinforcing materials are made from a variety of materials such asglass fibers, paper, plastics such as aromatic polyamides, graphite,glass, quartz, carbon, boron fibers, and organic fibers such as forinstance aramid, teflon, syndiotactic polystyrene, more particularly tomake laminates for printed wiring boards. In one preferred embodiment,the reinforcing materials include glass or fiberglass, in cloth or webform. As an illustration of the present application, the epoxy resincomposition according to the present invention are highly suitable forimpregnating, for example, woven glass fabric.

In one embodiment of the present invention, the reinforcing material iscontacted with the epoxy resin composition of the present invention in abath. Preferably the bath contains from about 40 to about 90 percentsolids. In such a bath, the various components of the epoxy resincomposition are dissolved or suspended in the bath. A single solvent orsolvent blend may be used for the bath, but in many applications aseparate solvent is used for each component added to the mixture. It ispreferable that the various solvents used be miscible with one another.Such solvents or diluents, include those which are volatile and escapefrom the composition prior to cure. Preferred solvents for the epoxyresins are ketones, including acetone and methyl ethyl ketone. Preferredsolvents for the hardener composition are slightly polar solvents,amides, for example, dimethylformamide, ether alcohols, for example,methyl, ethyl, propyl or butyl ethers of ethylene glycol, ketones ofmethyl, ethyl, propyl or butyl, dipropylene glycol, ethylene glycolmonomethylether, 1 methoxy-2-propanol, toluene, xylene methoxypropylacetate, 2-ethoxyethyl acetate, and mixtures of solvents. The catalystsand inhibitors, for example, are preferably dissolved in polar solvents,in particular alcohols, preferably lower alkanols and most preferablymethanol. Where the inhibitor is liquid or has high solubility innon-polar solvents, ketones may be used.

In one embodiment of the present invention, prepregs are prepared fromthe epoxy resin composition of the present invention and the reinforcingmaterial by a process comprising first contacting the reinforcingmaterial with an intimately mixed bath of the epoxy resin compositioncomprising: a polyepoxide in a solvent; a hardener composition of thepresent invention for the polyepoxide in a solvent; optionally, aninhibitor such as boric acid in a polar solvent; and optionally, acompound which catalyzes the curing of the polyepoxide with the hardenerin a polar solvent. The reinforcing material is impregnated with theepoxy resin composition in the bath. Thereafter, the resin impregnatedreinforcing material is passed through a heated zone at a temperaturesufficient to cause the solvents in the composition to evaporate, butbelow the temperature at which the polyepoxide undergoes complete cureduring the residence time in the heated zone.

The reinforcing material preferably has a residence time in the bath offrom about 0.1 minute to about 10 minutes, more preferably from about0.3 minute to about 8 minutes, and most preferably from about 0.5 minuteto about 3 minutes. The temperature of such bath is preferably fromabout 0° C. to about 100° C., more preferably from about 10° C. to about40° C. and most preferably from about 15° C. to about 30° C.

The residence time of the resin impregnated reinforcing material in theheated zone is from about 0.5 to about 15 minutes, more preferably fromabout 1 to about 10 minutes, and most preferably from about 1.5 to about5 minutes. The temperature of the heated zone is sufficient to cause anysolvents remaining in the epoxy resin composition to volatilize away,yet, not so high as to result in a complete curing of the components ofthe epoxy resin composition. Preferable temperatures of such heated zoneare from about 80° C. to about 230° C., more preferably from about 100°C. to about 200° C., and most preferably from about 150° C. to about180° C. Preferably, there is some means in the heated zone to remove thevolatile solvent, either by passing an inert gas through the heated zone(which can be an oven) or drawing a slight vacuum on the oven. In otherembodiments, the impregnated reinforcement materials may be exposed tozones of increasing temperature. For example, a first zone may bedesigned to cause the solvent to volatilize so the solvent can beremoved, with subsequent zones designed to result in partial cure of thepolyepoxide, that is, so called B-staging to form the prepreg.

In one embodiment of the present invention, laminates are manufacturedfrom the prepreg material prepared above by contacting several layers,segments or parts of the prepreg material with one another. Thereafter,the contacted layers, segments or parts are exposed to elevatedpressures and temperatures sufficient to cause the epoxy resin componentin the resin composition to fully cure such that the resin on adjacentlayers, segments or parts react to form a continuous epoxy resin matrixbetween and about the fibrous reinforcing material to form a laminate.Before being cured, the parts of prepreg material may be cut andstacked, or folded and stacked, into a part of desired shape andthickness.

The pressures used to press the prepregs, in a press means to prepare alaminate may be anywhere from about 10 to about 2000 newtons/cm², withfrom about 100 to about 1000 newtons/cm² being preferred. Thetemperature used to cure the prepreg material to form the laminates,depends upon the particular residence time, pressure used, and make upof the epoxy resin composition used. Generally, cure temperatures whichmay be used may be anywhere from about 100° C. to about 240° C.,preferably from about 120° C. to about 210° C., and more preferably fromabout 170° C. to about 200° C. The residence time of the prepregmaterial in the press may be anywhere from about 30 minutes to about 300minutes, preferably from about 45 to about 200 minutes, and morepreferably from about 60 minutes to about 120 minutes.

One embodiment of a process for making a laminate may be a continuousprocess. In such a continuous process, the reinforcing material is takenfrom the oven and appropriately arranged into the desired shape andthickness and pressed at very high temperatures for short times, inparticular such high temperatures are from about 180° C. to about 250°C., more preferably about 190° C. to about 210° C., at times of about 1minute to about 10 minutes.

In an alternative embodiment of the present invention, it may bedesirable to subject the laminate or final product to a post-cure stepoutside of the press. This post-cure step is designed to complete thecuring reaction. The post-cure step is usually performed at from about130° C. to about 220° C. for from about 20 minutes to about 200 minutes.This post-cure step may be performed in a vacuum to remove anycomponents which may volatilize.

The ultimate fully cured laminate prepared from the curable epoxy resincomposition of the present invention, often demonstrates a higher Tgthan laminates prepared from compositions not within the scope of thepresent invention. Generally, the Tg of the laminate is from about 150°C. to about 220° C., and preferably from about 170° C. to about 200° C.Usually the Tg is higher for the laminate of the present invention thanstandard FR4 laminates. It is known that the Tg of a laminate candecrease when a toughening agent is used. However, a fully curedlaminate using the resin composition of the present invention alsoexhibits improved toughness and less tendency to delaminate, whilemaintaining its Tg, than laminates prepared similarly using conventionalresins formulated to give similar gel times (hence similar reactivity).

A laminate prepared using the epoxy resin composition of the presentinvention, also maintains its excellent thermal properties such as forexample a high thermal resistance. For example, the Td is generally fromabout 300° C. to about 400° C., preferably from about 320° C. to about380° C. and more preferably greater than about 350° C.

The dielectric properties of a laminate, especially Dk, are alsoimproved when using the hardener composition of the present invention.When compared to standard FR4, the laminate of the present invention istypically better. The Dk is generally less than about 4.3, preferablyless than about 4.2 and more preferably less than 4.0. The Df isgenerally less than about 0.020 GHz, preferably less then about 0.015GHz and more preferably less than about 0.010 GHz.

In addition, a partly cured B-staged prepreg made from theepoxy/hardener composition of the present invention has improvedcosmetics and generates less dust during handling. Generally, theprepreg dust is less than about 0.15 g/m, preferably less than about0.10 g/m and more preferably less than about 0.08 g/m.

Furthermore, a fully cured C-staged laminate made from theepoxy/hardener composition of the present invention shows improvedtoughness and lower tendency to delamination. Generally, the presentinvention laminate shows at least a 10% improvement over laminates madefrom standard resins and up to ten times improvement. For example, thedelamination values of laminates of the present invention may be about1.0 J and above; and up to about 3.0 J. It is believed that PBMA or theblend of PBMA/SBM is acting as a toughening agent in the epoxy resincomposition. Because PBMA reacts with the epoxy groups, large phaseseparation is prevented.

The present invention will be further illustrated with reference to thefollowing Examples. The following Examples are set forth to illustratethe present invention and are not intended to limit the scope of thepresent invention. Unless otherwise stated all parts and percentages areby weight.

Various terms and designations for the materials used in the followingExamples are explained as follows:

Dowanol™ PMA is a propylene glycol monomethyl ether acetate sold by TheDow Chemical Company.

MEK stands for methyl ethyl ketone.

SMA stands for styrene maleic anhydride copolymer.

PBMA stands for maleinized polybutadiene.

SBM stands for styrene-butadiene-methyl methacrylate triblock polymer.

SMA 3000™ is a styrene-maleic anhydride copolymer with an averagemolecular weight (Mw) of 9500 and an anhydride equivalent weight of 393sold by Atofina.

Ricon™ 131MA10 is a maleinized polybutadiene with an average molecularweight (Mn) of 5000 and an anhydride equivalent weight of 981 sold bySartomer.

Ricon™ 130MA13 is a maleinized polybutadiene with an average molecularweight Mn of 2900 and an anhydride equivalent weight of 762 sold bySartomer.

SBM 1A17 is a styrene-butadiene-methyl methacrylate triblock polymersold by Atofina.

D.E.N.™ 438 is a multifunctional epoxy novolac with an epoxy equivalentweight of 180 sold by The Dow Chemical Company.

D.E.R.™ 560 is a brominated epoxy resin with an epoxy equivalent weightof 450 sold by The Dow Chemical Company.

M780 is a brominated epoxy resin with an epoxy equivalent weight of 470sold by Leuna Harze.

XU-19081.00 is an experimental brominated epoxy resin solution with anepoxy equivalent weight of 484 sold by The Dow Chemical Company.

Ken-React™ KR55 is a titanate adhesion promoter sold by KenrichPetrochemical Inc. 2E4MI stands for 2-ethyl-4-methyl imidazole solution(20% non volatiles).

Hycar™ CTBN 1300X13 is a liquid reactive rubber, which is a carboxylterminated butadiene-acrylonitrile copolymer with a molecular weight(Mn) of approximately 3150 and an average functionality of approximately1.8. (Hycar™ is a trademark of Noveon.) SBM 1A40 is astyrene-butadiene-methyl methacrylate triblock polymer sold by Atofina.

TBBA stands for tetrabromobisphenol A.

D.E.N.™ 431 is a multifunctional epoxy novolac with an epoxy equivalentweight of 176 sold by The Dow Chemical Company.

E.R.L.™ 4299 is a cycloaliphatic epoxy resin with an epoxy equivalentweight of 195 sold by The Dow Chemical Company.

Various experimental testing and analytical methods used for variousmeasurements in the following Examples are as follows:

DSC stands for differential scanning colorimetry. Tg is measured by themid-point Tg by DSC at a heating rate of 10° C./minute for films and ata heating rate of 20° C./minute for laminates. The method used wasIPC-TM-650-#2.4.25C.

T-300 stands for time to delamination at 300° C. measured bythermo-mechanical analysis (TMA). The method used wasIPC-TM-650-#2.4.24:1.

CTE stands for coefficient of thermal expansion measured by TMA.

Td stands for temperature of thermal degradation measured by thermogravimetrical analysis (TGA). Td is the temperature at 5 wt % loss.

CISCO test (288° C.) is a measurement of thermal shock resistance. Onecycle includes a solder dip at 288° C. for 10 seconds followed by aquenching in air at ambient temperature (25° C.) for 10 seconds (1cycle=20 seconds)

Energy of delamination on impact is the energy required to reachdelamination of the laminate on an impact. The equipment used in thistest is a Byk Chemie impact tester model N⁰5510. The indentor used is asteel punch (2 lb) with a hemispherical head (diameter=⅝ inches). Bygradually increasing the distance the weight drops, the height at whichdelamination occurs is determined (noted as Hd). The energy ofdelamination on impact (noted as E) is then calculated as follows:E=mass×distance×acceleration

-   -   E=0.2262 Hd, where Hd is measured in inch and E in joule.

The higher the value of E, the better the toughness of the laminate andthe higher the interlayer adhesion. This is also a measure ofbrittleness.

Copper peel strength was measured using the method described inIPC-TM-650-#2.4.8C.

TMA stands for thermo-mechanical analysis. The method used wasIPC-TM-650-#2.4.24C.

Prepreg dust was measured as follows: About 20 sheets of prepreg havinga width of about 30 cm were cut with a guillotine. The resulting dustcoming off the prepreg was thoroughly collected and weighed. The weightof the prepreg dust was normalized to the total cutting distance (g/m).

EXAMPLE 1

In this example, an anhydride hardener solution of the present inventionwas prepared in a 5L glass reactor, equipped with a mechanical stirrer,a heating jacket, a N₂ inlet and a dropping funnel. 1821.3 g of Dowanol*PMA and 40.3 g of SBM 1A17 were charged in the reactor and heated to 90°C. After the solids were completely dissolved, 1554.8 g of SMA 3000 wasadded to the solution. After the solids were completely dissolved, 201.3g of Ricon* 131MA10 was added to the solution. Then the solution turnedinto a white turbid solution but was homogeneous. After 30 minutes, thesolution was allowed to cool down to a temperature of 80° C. and MEK wasintroduced into the solution at 80° C. After complete cooling of thesolution to ambient temperature (−25° C.), the anhydride hardenersolution was turbid whitish homogeneous. The hardener solution remainedstable during a testing period of 2 months without phase separation norsettling. The theoretical anhydride equivalent weight of the anhydridehardener solution was 432 (based on solids).

COMPARATIVE EXAMPLE A

A standard anhydride hardener solution was prepared in a 5L glassreactor, equipped with a mechanical stirrer, a heating jacket, a N₂inlet and a dropping funnel. 2000.0 g of Dowanol* PMA and 2000.0 g ofSMA 3000 were charged in the reactor and heated to 90° C. Thirty minutesafter the solids completely dissolved, the solution was allowed to cooldown to ambient temperature (−25° C.). The anhydride hardener solutionwas clear pale yellow. The theoretical anhydride equivalent weight ofthe anhydride hardener solution was 393 (based on solids).

EXAMPLE 2

An anhydride hardener solution was prepared using the same procedure asdescribed in Example 1. The anhydride hardener composition included1821.3 g of cyclohexanone, 1510.0 g of SMA 3000, 238.7 g of Ricon*130MA13, 47.7 g of SBM 1A17 and 364.3 g of MEK. The resulting anhydridehardener solution was turbid whitish homogeneous. The hardener solutionremained stable during a testing period of 2 months without phaseseparation nor settling. The theoretical anhydride equivalent weight ofthe hardener solution was 431 (based on solids).

EXAMLE 3

An anhydride hardener solution was prepared using the same procedure asdescribed in Example 1. The anhydride hardener composition included1821.3 g of cyclohexanone, 1490.6 g of SMA 3000, 254.9 g of Ricon*131MA10, 51.0 g of SBM 1A17 and 364.3 g of MEK. The anhydride hardenersolution was turbid whitish homogeneous. The hardener solution remainedstable during a testing period of 2 months without phase separation norsettling. The theoretical anhydride equivalent weight of the hardenersolution was 444 (based on solids).

EXAMPLE 4

An anhydride hardener solution was prepared using the same procedure asdescribed in Example 1. The anhydride hardener composition included1216.3 g of Dowanol* PMA, 1216.3 g of SMA 3000, 168.7 g of Ricon*131MA10, 29.2 g of SBM 1A17 and 285.5 g of MEK. The anhydride hardenersolution was turbid whitish homogeneous. The hardener solution remainedstable during a testing period of 2 months without phase separation norsettling. The theoretical anhydride equivalent weight of the hardenersolution was 433 (based on solids).

EXAMPLE 5

An anhydride hardener solution was prepared using the same procedure asdescribed in Example 1. The anhydride hardener composition included1122.2 g of Dowanol* PMA, 1050.3 g of SMA 3000, 60.7 g of Ricon*131MA10, 12.1 g of SBM 1A17 and 112.8 g of MEK. The anhydride hardenersolution was turbid whitish homogeneous. The hardener solution remainedstable during a testing period of 2 months without phase separation norsettling. The theoretical anhydride equivalent weight of the hardenersolution was 414 (based on solids).

EXAMPLE 6

An anhydride hardener solution was prepared using the same procedure asdescribed in Example 1. The anhydride hardener composition included1818.2 g of Dowanol* PMA, 1718.9 g of SMA 3000, 134.4 g of Ricon*131MA10, 99.9 g of Ricon* 130MA13, 46.9 g of SBM 1A17 and 181.8 g ofMEK. The anhydride hardener solution was turbid whitish homogeneous. Thehardener solution remained stable during a testing period of 2 monthswithout phase separation nor settling. The theoretical anhydrideequivalent weight of the hardener solution was 430 (based on solids).

EXAMPLE 7 AND COMPARATIVE EXAMPLE B

In this example, prepregs and laminates were prepared by curing an epoxysolution (XU-19081.00 commercially available from The Dow ChemicalCompany) with the anhydride hardener solutions described in ComparativeExample A and Example 1. The properties of the resulting prepregs andlaminates were then compared.

Prepregs were produced by coating a varnish solution, as described inTable I, on woven glass (standard E-glass) and then drying and curingthe varnish to an intermediate advancement point (B-stage prepreg) usinga 3-meter long horizontal treater operating at 174° C. with a forced airflow. Prepregs were cut in sheets of 30 cm×30 cm.

Laminates were then prepared as follows: Eight sheets of prepregs werestacked together between copper foil and placed into a press. The sheetsof prepregs were fully cured in the press at 190° C. for 90 minutesunder 25,000 lbs of pressure. Depending on the melt viscosity of theprepreg powder, the pressure was adjusted to obtain enough flow, andtherefore, a laminate thickness of about 1.5±0.1 mm. The copper foillayers were optionally etched to obtain unclad laminates. The resincontent of the resulting laminates was about 43±3%. TABLE I Varnish 1Varnish 2 Components (Comparative Example B) (Example 7) CompositionsXU-19081 3132.4 g 3561.9 g (85% non volatiles) Anhydride hardener 2269.3g solution from Comparative Example A Anhydride hardener 2112.7 gsolution from Example 1 Boric acid solution 17.5 g 17.0 g (20% nonvolatiles) 2E4MI 6.99 g 6.80 g Properties of Varnish Varnish appearanceClear, pale Turbid, yellow whitish, homogeneous, stable Stroke curereactivity 271 seconds 275 seconds at 170° C. DSC film Tg ^((a)) 180.7°C. 184.4° C. Film appearance Clear, brittle, Opalescent, bubbles lessbrittle, less bubbles Properties of Prepreg Prepreg appearance Regular,Regular, shiny, prepreg powder flexible, easy to take off, prepregpowder dusty prepreg difficult to (“mushroom” effect) take off, non-dusty prepreg (no “mushroom” effect) Prepreg dust 0.172 g/m 0.064 g/mPrepreg stability at Prepreg sheets Prepreg sheets 40° C. under a do notstick do not stick 3 kg load together after together after 1 week 1 weekProperties of Laminates Laminate appearance Yellow, Yellow, translucenttranslucent DSC Tg (laminate) 185.6° C. 186.8° C. CTE < Tg 74 ppm/K 84ppm/K CTE > Tg 233 ppm/K 257 ppm/K T 300 42 minutes 46 minutes Cu peel8.2 N/cm 9.3 N/cm Solder dip at 288° C. >6 minutes >6 minutes CISCO test(288° C.) >6 minutes >10 minutes (>18 cycles) (>30 cycles) Td 369° C.369° C. E(Energy of 0.34 J 1.36 J delamination on impact test) Dk at 1MHz 4.25 3.67 Dk at 100 MHz 4.17 3.62 Dk at 1 GHz 4.09 3.52 Df at 1 MHz0.006 0.008 Df at 100 MHz 0.006 0.006 Df at 1 GHz 0.007 0.006^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate.

The results in Table I above shows that using the anhydride hardener ofthe present invention significantly improves the properties of a systemas compared to using a standard anhydride hardener, both for a prepregand for a laminate. The anhydride hardener of the present invention ledto a much less dusty prepreg which is consequently much easier tohandle. The hardener of the present invention also greatly increased thelaminate toughness, the energy of delamination on impact being 4 timeshigher than for the laminate of Comparative Example A. The dielectricconstants, especially Dk, were lower when the anhydride hardenersolution of Example 1 was used. The excellent thermal properties of thelaminate were also maintained using the hardener of the presentinvention.

COMPARATIVE EXAMPLE C

This example describes the properties of prepregs and laminates preparedfrom curing Leuna M780 epoxy solution with the anhydride hardenersolution described in Comparative Example A.

Prepregs and laminates were prepared using the same procedure asdescribed in Example 7, except that the press was operated at 32,000 lbsof pressure. TABLE II Varnish 3 Components (Comparative Example C)Composition Leuna M780 solution 2343.7 g (70% non volatiles) Anhydridehardener 2888.0 g solution from Comparative Example A Boric acidsolution 61.7 g (20% non volatiles) 2E4MI 15.4 g Properties of VarnishVarnish appearance Clear yellow Stroke cure reactivity 242 seconds at170° C. DSC film Tg ^((a)) 187.4° C. Properties of Prepreg Prepregappearance Foamy, prepreg powder easy to take off (“mushroom” effect)Prepreg dust 0.284 g/m Prepreg stability at 40° C. Prepreg sheets do notunder a 3 kg load stick together after 1 week Properties of LaminatesLaminate appearance Yellow, opalescent DSC Tg (laminate) 187.3° C. CTE <Tg 54 ppm/K CTE > Tg 223 ppm/K T 300 >30 minutes Solder dip at 288°C. >3 minutes E(Energy of delamination 0.90 J on impact test)^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate

The results in Table II above show that the use of a standard anhydridehardener led to a dusty prepreg and a brittle laminate.

EXAMPLE 8

This example describes the properties of prepregs and laminates preparedfrom curing DER*560 epoxy solution with the anhydride hardener solutiondescribed in Example 2.

Prepregs and laminates were prepared using the same procedure asdescribed in Example 7, except that the press was operated at 60,000 lbsof pressure. TABLE III Varnish 4 Components (Example 8) CompositionDER*560 solution 2355.6 g (65% non volatiles) Anhydride hardener 3258.8g solution from Example 2 Boric acid solution 14.7 g (20% non volatiles)2E4MI 12.0 g Properties of Varnish Varnish appearance Clear, darkyellow, stable, homogeneous Stroke cure reactivity 270 seconds at 170°C. DSC film Tg ^((a)) 179.9° C. Properties of Prepreg Prepreg appearanceShiny, flexible, prepreg powder difficult to take off (no “mushroom”effect) Prepreg dust 0.031 g/m Prepreg stability at 40° C. Prepregsheets do not under a 3 kg load stick together after 1 week Propertiesof Laminates Laminate appearance Yellow, opaque UL 94 rating V-0 DSC Tg(laminate) 184.1° C. CTE < Tg 52 ppm/K CTE > Tg 204 ppm/K T 300 >30minutes Td 368° C. Solder dip at 288° C. >5 min. CISCO test (288°C.) >10 minutes (>30 cycles) E(Energy of delamination 2.26 J on impacttest) Dk at 1 MHz 3.91 Dk at 100 MHz 3.83 Dk at 1 GHz 3.75 Df at 1 MHz0.008 Df at 100 MHz 0.007 Df at 1 GHz 0.009^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate

The results in Table III above show that the use of the anhydridehardener of the present invention significantly improved the systemproperties compared to a standard anhydride hardener, both for theprepreg and for the laminate. The anhydride hardener led to much lessdusty prepreg, 9 times less prepreg dust is generated during cuttingcompared to the Comparative Example C, which is consequently much easierto handle. It also greatly increased the laminate toughness, the energyof delamination on impact being 2.5 times higher than for theComparative Example C. The excellent thermal properties and dielectricconstants were maintained.

EXAMPLE 9

This example describes the properties of prepregs and laminates preparedfrom curing DER*560 epoxy solution with the anhydride hardener solutiondescribed in Example 3.

Prepregs and laminates were prepared using the same procedure asdescribed in Example 7, except that the press was operated at 45,000 lbsof pressure. TABLE IV Varnish 5 Components (Example 9) CompositionDER*560 solution 2321.3 g (65% non volatiles) Anhydride hardener 3293.4g solution from Example 3 Boric acid solution 14.9 g (20% non volatiles)2E4MI 12.0 g Properties of Varnish Varnish appearance Whitish yellow,homogeneous, stable Stroke cure reactivity 274 seconds at 170° C. DSCfilm Tg ^((a)) 184.9° C. Properties of Prepreg Prepreg appearance Shiny,flexible, prepreg powder difficult to take off (no “mushroom” effect)Prepreg stability at 40° C. Prepreg sheets do not under a 3 kg loadstick together after 1 week Properties of Laminates Laminate appearanceYellow, opaque UL 94 rating V-0 T 300 >30 minutes Td 365° C. Solder dipat 288° C. >6 minutes CISCO test (288° C.) >6 minutes (>18 cycles)E(Energy of delamination 2.83 J on impact test) Dk at 1 MHz 3.72 Dk at100 MHz 3.65 Dk at 1 GHz 3.58 Df at 1 MHz 0.006 Df at 100 MHz 0.006 Dfat 1 GHz 0.011^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate

The results in Table IV above show that the use of the anhydridehardener of the present invention significantly improved the systemproperties compared to a standard anhydride hardener, both for theprepreg and for the laminate. The anhydride hardener of the presentinvention led to a much less dusty prepreg which is consequently mucheasier to handle. It also greatly increased the laminate toughness, theenergy of delamination on impact being 3.1 times higher than for theComparative Example C. The excellent thermal properties and dielectricconstants were kept.

EXAMPLE 10

This example describes the properties of prepregs and laminates preparedfrom curing Leuna M780 epoxy solution with the anhydride hardenersolution described in Example 4.

Prepregs and laminates were prepared using the same procedure asdescribed in Example 7, except that the press was operated at 30,000 lbsof pressure. TABLE V Varnish 6 Components (Example 10) Composition LeunaM780 solution 2193.4 g (70% non volatiles) Anhydride hardener 2915.8 gsolution from Example 4 KR55 24.3 g Boric acid solution 58.4 g (20% nonvolatiles) 2E4MI 14.6 g Properties of Varnish Varnish appearance Turbid,whitish, homogeneous, stable Stroke cure reactivity 208 seconds at 170°C. DSC film Tg ^((a)) 170.7° C. Properties of Prepreg Prepreg appearanceShiny, flexible, prepreg powder difficult to take off (no “mushroom”effect) Properties of Laminates Laminate appearance Yellow whitish,opaque DSC Tg (laminate) 183.2° C. CTE < Tg 57 ppm/K CTE > Tg 220 ppm/KCu peel 10.3 N/cm Solder dip at 288° C. >5 minutes CISCO test (288°C.) >5 minutes E(Energy of delamination 1.36 J on impact test) Dk at 1MHz 4.25 Dk at 100 MHz 4.20 Dk at 1 GHz 4.10 Df at 1 MHz 0.0095 Df at100 MHz 0.010 Df at 1 GHz 0.0095^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate

The results in Table VI above show that the use of the anhydridehardener of the present invention led to a non-dusty prepreg which isconsequently easy to handle. It also led to a good laminate toughness.The thermal properties and the dielectric constant were excellent.

EXAMPLE 11

This example describes the properties of prepregs and laminates preparedfrom curing Leuna M780 epoxy solution with the anhydride hardenersolution described in Example 5.

Prepregs and laminates were prepared using the same procedure asdescribed in Example 7, except that the press was operated at 30,000 lbsof pressure. TABLE VI Varnish 7 Components (Example 12) CompositionLeuna M780 solution 1799.0 g (70% non volatiles) Anhydride hardener2380.7 g solution from Example 5 KR55 39.8 g Boric acid solution 47.7 g(20% non volatiles) 2E4MI 10.7 g Properties of Varnish Varnishappearance Yellow, homogeneous, stable, opalescent Stroke curereactivity 259 seconds at 170° C. DSC film Tg ^((a)) 170.0° C.Properties of Prepreg Prepreg appearance Relatively foamy, prepregpowder relatively easy to take off (small “mushroom” effect) Propertiesof Laminates Laminate appearance Yellow, opalescent DSC Tg (laminate)178.7° C. E(Energy of delamination 1.13 J on impact test) Dk at 1 MHz4.29 Dk at 100 MHz 4.21 Dk at 1 GHz 4.16 Df at 1 MHz 0.009 Df at 100 MHz0.007 Df at 1 GHz 0.010^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate

The results show that the use of the anhydride hardener of the presentinvention led to a good laminate toughness. The thermal properties andthe dielectric constant were excellent.

EXAMPLE 12

This example describes the properties of prepregs and laminates preparedfrom curing a blend of DER*560 and DEN*438 epoxy solution with theanhydride hardener solution described in Example 6.

Prepregs and laminates were prepared using the same procedure asdescribed in Example 7, except that the press was operated at 23,000 lbsof pressure. TABLE VII Varnish 8 Components Example 12 CompositionDER*560 solution 1967.1 g (65% non volatiles) DEN*438 175.2 g Anhydridehardener solution 3277.6 from ion was 414 (based on solids). Example 7Boric acid solution 29.2 g (20% non volatiles) 2E4MI 7.7 g Properties ofVarnish Varnish appearance Yellow, homogeneous, stable, turbid Strokecure reactivity 276 seconds at 170° C. DSC film Tg ^((a)) 182.9° C.Properties of Prepreg Prepreg appearance Shiny, flexible, prepreg powderdifficult to take off (no “mushroom” effect) Properties of LaminatesLaminate appearance Yellow, opalescent DSC Tg (laminate) 181.1° C. CTE <Tg 68 ppm/K CTE > Tg 163 ppm/K T 300 >30 minutes Cu peel 8.2 N/cmE(Energy of delamination 2.26 J on impact test) Dk at 1 MHz 3.73 Dk at100 MHz 3.67 Dk at 1 GHz 3.63 Df at 1 MHz 0.005 Df at 100 MHz 0.007 Dfat 1 GHz 0.011^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. onhot plate

The results in Table VII above show that the use of the anhydridehardener of the present invention led to a good laminate toughness. Thethermal properties and the dielectric constant were excellent.

EXAMPLE 13

An anhydride hardener solution was prepared using the same procedure asdescribed in Example 1. The anhydride hardener composition included1750.0 g of Dowanol* PMA, 1857.1 g of SMA 3000, 215.9 g of Ricon*131MA10, 27.0 g of SBM 1A40 and 350.0 g of MEK. The anhydride hardenersolution was turbid whitish and homogeneous. The hardener solutionremained stable during a testing period of 2 months without phaseseparation nor settling. The theoretical anhydride equivalent weight ofthe hardener solution was 424 (based on solids).

EXAMPLE 14

An anhydride hardener solution was prepared using the same procedure asdescribed in Example 1. The anhydride hardener composition included1800.0 g of Dowanol* PMA, 1449.2 g of SMA 3000, 215.0 g of Ricon*130MA13, 35.8 g of SBM 1A17 and 300.0 g of MEK. The anhydride hardenersolution was turbid whitish homogeneous. The hardener solution remainedstable during a testing period of 2 months without phase separation norsettling. The theoretical anhydride equivalent weight of the hardenersolution was 420 (based on solids).

EXAMPLE 15

An anhydride hardener solution was prepared using the same procedure asdescribed in Example 1. The anhydride hardener composition included3671.9 g of Dowanol* PMA, 3623.2 g of SMA 3000, 730.7 g of Ricon*130MA13, 146.1 g of SBM 1A17 and 828.1 g of MEK. The anhydride hardenersolution was turbid whitish homogeneous. The hardener solution remainedstable during a testing period of 2 months without phase separation norsettling. The theoretical anhydride equivalent weight of the hardenersolution was 439 (based on solids).

COMPARATIVE EXAMPLE D

This example describes the properties of prepregs and laminates preparedfrom curing an epoxy solution (XU-19081.00 commercially available fromThe Dow Chemical Company) with the anhydride hardener described inComparative Example A and with 5 phr of a liquid rubber toughening agentCTBN 1300X13. Prepregs were produced by coating a varnish solution asdescribed in Table VIII on woven glass (standard E-glass) by hand lay-uptechnique and then drying and curing the coated woven glass to anintermediate advancement point (B-stage prepreg) using a ventilated ovenoperating at 175° C. with a forced air flow. Laminates were prepared bycutting prepregs in sheets of 30 cm×30 cm and then copper foils werepressed in between the prepregs as described in Example 7.

This Comparative Example D may be compared with Example 7 andComparative Example B. TABLE VIII Varnish 9 Components (ComparativeExample D) Composition XU-19081 (85% non volatiles) 165.6 g Anhydridehardener 134.4 g from Example 1 CTBN 1300X13 solution 15.0 g (60% nonvolatiles) Boric acid solution 0.30 g (20% non volatiles) 2E-4MI 0.12 gProperties of Varnish Varnish appearance Translucent Stroke curereactivity at 170° C. 306 seconds DSC film Tg ^((a)) 157° C. Filmappearance ^((a)) Opalescent, less brittle, less bubbles thanComparative Example B Properties of Prepreg Prepreg appearance Regular,relatively dusty Prepreg stability at 40° C. Prepreg sheets sticks undera 3 kg load together after 1 week Properties of Laminates DSC laminateTg 168° C. Cu peel 8.6 N/cm E(Energy of delamination 0.57 J on impacttest)^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate

The results in Table VIII above show that the use of a liquid rubbertoughening agent improved some properties compared to the referencesystem produced with Varnish 1 Comparative Example B (toughening, copperpeel strength), but also dramatically impacted some other properties(Tg, prepreg stability at 40° C.). The use of improved anhydridehardener as described in Varnish 2 (Example 7) led to much betteroverall performances.

EXAMPLE 16

This example describes the properties of prepregs and laminates preparedfrom curing a DEN*431 epoxy solution with TBBA and the anhydridesolution described in Example 13.

Prepregs and laminates were prepared using the same procedure asdescribed in Example 7. TABLE IX Varnish 10 Components (Example 16)Composition DEN*431 solution 1968.1 g (67.3% non volatiles) TBBA 1135.4g Anhydride hardener 2307.1 g solution from Example 13 Boric acidsolution 23.45 g (20% non volatiles) MEK 310.8 g 2E4MI 6.12 g Propertiesof Varnish Varnish appearance Yellow opalescent Stroke cure reactivity235 seconds at 170° C. DSC film Tg ^((a)) 168.7° C. Film appearance^((a)) Yellow opalescent Properties of Prepreg Prepreg appearance Niceshiny, prepreg powder difficult to take off (no “mushroom” effect)Prepreg stability at 40° C. Prepreg sheets stick under a 3 kg loadtogether after 1 week Properties of Laminates Laminate appearance Yellowopalescent DSC laminate Tg 167.9° C. Cu peel 12.2 N/cm^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate

The results in Table IX above show that the use of the anhydridehardener of the present invention with the blend of DEN*431 and TBBA ledto nice prepreg with relatively good adhesion to copper.

EXAMPLE 17

This example describes the properties of prepregs and laminates preparedfrom curing a blend of DER*560 and DEN*438 epoxy solution with theanhydride hardener solution described in Example 14.

Prepregs and laminates were prepared using the same procedure asdescribed in Example 7. TABLE X Varnish 11 Components (Example 17)Composition DER*560 solution (65% non volatiles) 2891.1 g DEN*438solution 366.3 g (70.3% non volatiles) Anhydride hardener 4705.0 gsolution from Example 14 Boric acid (20% non volatiles) 42.9 g 2E4MI11.24 g Properties of Varnish Varnish appearance Yellowish opalescentStroke cure reactivity at 170° C. 276 seconds DSC film Tg ^((a)) 179° C.Properties of Prepreg Prepreg appearance Shiny, prepreg powder difficultto take off (no “mushroom” effect) Prepreg dust 0.100 g/m Prepregstability at 40° C. Prepreg sheets do not under a 3 kg load sticktogether after 1 week Properties of Laminates Laminate appearanceWhitish opaque DSC Tg (laminate) 179.6° C. CTE < Tg 84 ppm/K CTE > Tg269 ppm/K T 300 32 minutes Cu peel 9.0 N/cm UL 94 rating V-0 Td 366° C.^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate

The results in Table X above show that the use of the anhydride hardenerof the present invention led to a laminate with excellent overallproperties.

EXAMPLE 18

This example describes the properties of prepregs and laminates preparedfrom curing a blend of DER*560 and ERL-4299 epoxy solution with theanhydride hardener solution described in Example 14.

Prepregs and laminates were prepared using the same procedure asdescribed in Example 7. TABLE XI Varnish 12 Components (Example 18)Composition DER*560 solution 2327.4 g (65% non volatiles) ERL-4299solution 294.9 g (70.3% non volatiles) Anhydride hardener 3542.5 gsolution from Example 14 Boric acid (20% non volatiles) 34.5 g 2E4MI8.75 g Properties of Varnish Varnish appearance Opalescent to opaquehomogeneous, yellowish, low viscosity Stroke cure reactivity 263 secondsat 170° C. DSC film Tg ^((a)) 182.6° C. Properties of Prepreg Prepregappearance Nice shiny Properties of Laminates Laminate appearanceYellowish opalescent DSC Tg (laminate) 178.3° C. Cu peel 7.2 N/cm UL 94rating V-1 Dk at 1 MHz 3.79 Dk at 100 MHz 3.70 Dk at 1 GHz 3.68 Df at 1MHz 0.0066 Df at 100 MHz 0.0075 Df at 1 GHz 0.0083^((a)) Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate

The results in Table XI above show that the use of the anhydridehardener of the present invention led to laminate with excellent thermaland electrical properties.

EXAMPLE 19

This example describes the properties of prepregs and laminates preparedfrom curing a blend of DER*560 and DEN*438 epoxy solution with theanhydride hardener solution described in Example 15.

Prepregs and laminates were prepared using the same procedure asdescribed in Example 7. TABLE XII Varnish 13 Components (Example 19)Composition DER*560 solution 2205.3 g (65% non volatiles) DEN* 438solution 292.5 g (68% non volatiles) Anhydride hardener 3683.9 gsolution from Example 15 3-glycidyloxypropyl 17.5 g trimethoxysilaneBoric acid (20% non volatiles) 33.1 g 2E4MI 7.87 g Properties of VarnishVarnish appearance Light orange opaque Stroke cure reactivity 207seconds at 170° C. DSC film Tg^((a)) 175.4° C. Properties of PrepregPrepreg appearance Nice shiny regular Properties of Laminates Laminateappearance Whitish opaque DSC Tg (laminate) 180.3° C. Cu peel 7.8 N/cmDSC Tg (laminate 182.5° C. with treated copper^((b))) Cu peel (laminate16.0 N/cm with treated copper^((b)))^((a))Curing schedule: 10 minutes at 170° C. + 90 minutes at 190° C. ona hot plate;^((b))resin coated copper foil (epoxy resin = DER*592-A80, B-staged)

The results in Table XII above show that the use of the anhydridehardener of the present invention led to a laminate with good thermalproperties and excellent adhesion on resin coated copper foil.

1. A hardener composition useful for curing a polyepoxide resincomprising a blend of (a) a carboxylic anhydride which is a copolymer ofan ethylenically unsaturated anhydride and a vinyl compound; (b) acopolymer of an ethylenically unsaturated anhydride and an elastomer;and (c) a stabilizing agent to prevent phase separation of components(a) and (b).
 2. The hardener composition of claim 1 wherein thecopolymer of an ethylenically unsaturated anhydride and a vinyl compoundis a copolymer of styrene and maleic anhydride (SMA).
 3. The hardenercomposition of claim 1 wherein the copolymer of an ethylenicallyunsaturated anhydride and an elastomer is a maleic anhydride-modifiedpolybutadiene (PBMA).
 4. The hardener composition of claim 1 wherein thestabilizing agent is a block copolymer
 5. The hardener composition ofclaim 1 wherein the stabilizing agent is a triblock copolymer ofstyrene-butadiene-methyl methacrylate (SBM).
 6. The hardener compositionof claim 1 including (d) a solvent.
 7. The hardener composition of claim1 including (e) a cure inhibitor.
 8. The hardener composition of claim 7wherein the cure inhibitor is boric acid.
 9. The hardener composition ofclaim 1 wherein the amount of the carboxylic anhydride which is acopolymer of an ethylenically unsaturated anhydride and a vinyl compoundpresent in the composition is such that the epoxy to anhydride molarratio is between about 0.8:1.0 and about 1.2:1.0.
 10. The hardenercomposition of claim 1 wherein the amount of component (b) present inthe composition is such that the component (a) to component (b) weightratio is between about 95:5 and about 80:20.
 11. The hardenercomposition of claim 1 wherein the amount of stabilizing agent presentin the composition is such that the component (b) to component (c)weight ratio is between about 60:40 and about 95:5.
 12. A process forpreparing a hardener composition comprising mixing (a) a carboxylicanhydride which is a copolymer of an ethylenically unsaturated anhydrideand a vinyl compound; (b) a copolymer of an ethylenically unsaturatedanhydride of an elastomer; and (c) a stabilizing agent to prevent phaseseparation of components (a) and (b).